California Code, Labor Code - LAB § 3861

(a) Except as provided in subdivision (b), the appeals board is empowered to and shall allow, as a credit to the employer to be applied against their liability for compensation, such amount of any recovery by the employee for their injury, either by settlement or after judgment, as has not theretofore been applied to the payment of expenses or attorneys' fees, pursuant to the provisions of Sections 3856, 3858, and 3860, or has not been applied to reimburse the employer.

(b) In a claim subject to subdivision (b) of Section 3852, the employer shall not assert, claim, or enforce any credit or offset against any future workers' compensation benefits, including, but not limited to, future indemnity, medical, and vocational rehabilitation benefits, based on the employee's civil recovery from a third-party tortfeasor.  The appeals board is not empowered and shall not allow such a credit to be applied to the employer.